In the first above-identified previously filed patent application, a new concept is disclosed for determining the state of hemoglobin oxygen saturation in brain tissue, particularly fetal brain tissue, that is especially useful during the critical time of childbirth. Basically, this approach utilizes the concept of injecting a very short pulse of light at a selected wavelength in the near-infrared range (e.g. one nanosecond (ns) in length) into the head via a fiberoptic cable optically coupled to the head, detecting the corresponding photons emerging from the head into an adjacent detector and fiberoptic cable after a first very short period (e.g., one ns) and then detecting emerging photons once again after at least one more very brief period (on the order of 4 to 5 ns).
The injected pulse of photons (sometimes referred to as a “bolus”) spreads out from the injection site in the form of a rapidly expanding “glowball,” due to the extensive amount of scatter which occurs in this medium (on average, photon direction becoming completely randomized after only 0.6 mm of travel), and this translates into photon pathlength. Therefore, the detection of differing amounts of photons leaving the head at different relatively short intervals corresponding to photon travel over different effective pathlengths within the brain, which represents, and characterizes, differing depths of photon travel within the brain tissue. Thus, the quantities of photons detected at different intervals in effect sample different depths of travel, and hence different volumes of brain tissue. As a result, mathematical processing and correlation of these differential results will be directly indicative of differing amounts of photon absorption at different depths, including the amount of photon reduction which results (for example) from absorption by hemoglobin molecules. By using selected wavelengths of injected light, the amount of hemoglobin oxygenation can thus be determined, due to the difference in oxygen absorption as opposed to reduced or non-oxygenated hemoglobin, on a wavelength-specific basis.
The aforementioned U.S. Pat. No. 6,381,480 discloses this technological concept in considerably greater detail, together with representative and then-contemplated preferred embodiments of apparatus and methodology for implementing the concept to create a useful fetal cerebral oximeter. As may be seen by further study of that patent, it will be seen that the disclosed apparatus basically includes a source of photons coupled to the head by a fiberoptic conductor which leads to an injection site (e.g., the forehead), plus a fiberoptic leading from a photon detection device that basically comprises at least two shuttered detectors which are gated open for a very brief period (on the order of ins) at specific time intervals after the instant of injection, preferably by using a trigger signal obtained from a fiberoptic conductor that transmits a small fraction of the photons emitted by the source to the shuttered detectors at different and specifically timed intervals.